/*
    cdecoder.c - c source to a base64 decoding algorithm implementation

    This is part of the libb64 project, and has been placed in the public domain.
    For details, see http://sourceforge.net/projects/libb64
*/

#include <pgmspace.h>
#include <stdint.h>
#include "cdecode.h"

extern "C" {

    static int base64_decode_value_signed(int8_t value_in) {
        static const int8_t decoding[] PROGMEM  = {62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51};
        static const int8_t decoding_size = sizeof(decoding);
        value_in -= 43;
        if (value_in < 0 || value_in > decoding_size) {
            return -1;
        }
        return pgm_read_byte(&decoding[(int)value_in]);
    }

    void base64_init_decodestate(base64_decodestate* state_in) {
        state_in->step = step_a;
        state_in->plainchar = 0;
    }

    static int base64_decode_block_signed(const int8_t* code_in, const int length_in, int8_t* plaintext_out, base64_decodestate* state_in) {
        const int8_t* codechar = code_in;
        int8_t* plainchar = plaintext_out;
        int8_t fragment;

        *plainchar = state_in->plainchar;

        switch (state_in->step) {
            while (1) {
            case step_a:
                do {
                    if (codechar == code_in + length_in) {
                        state_in->step = step_a;
                        state_in->plainchar = *plainchar;
                        return plainchar - plaintext_out;
                    }
                    fragment = (int8_t)base64_decode_value_signed(*codechar++);
                } while (fragment < 0);
                *plainchar    = (fragment & 0x03f) << 2;
            // falls through
            case step_b:
                do {
                    if (codechar == code_in + length_in) {
                        state_in->step = step_b;
                        state_in->plainchar = *plainchar;
                        return plainchar - plaintext_out;
                    }
                    fragment = (int8_t)base64_decode_value_signed(*codechar++);
                } while (fragment < 0);
                *plainchar++ |= (fragment & 0x030) >> 4;
                *plainchar    = (fragment & 0x00f) << 4;
            // falls through
            case step_c:
                do {
                    if (codechar == code_in + length_in) {
                        state_in->step = step_c;
                        state_in->plainchar = *plainchar;
                        return plainchar - plaintext_out;
                    }
                    fragment = (int8_t)base64_decode_value_signed(*codechar++);
                } while (fragment < 0);
                *plainchar++ |= (fragment & 0x03c) >> 2;
                *plainchar    = (fragment & 0x003) << 6;
            // falls through
            case step_d:
                do {
                    if (codechar == code_in + length_in) {
                        state_in->step = step_d;
                        state_in->plainchar = *plainchar;
                        return plainchar - plaintext_out;
                    }
                    fragment = (int8_t)base64_decode_value_signed(*codechar++);
                } while (fragment < 0);
                *plainchar++   |= (fragment & 0x03f);
            }
        }
        /* control should not reach here */
        return plainchar - plaintext_out;
    }

    static int base64_decode_chars_signed(const int8_t* code_in, const int length_in, int8_t* plaintext_out) {
        base64_decodestate _state;
        base64_init_decodestate(&_state);
        int len = base64_decode_block_signed(code_in, length_in, plaintext_out, &_state);
        if (len > 0) {
            plaintext_out[len] = 0;
        }
        return len;
    }

    int base64_decode_value(char value_in) {
        return base64_decode_value_signed(*((int8_t *) &value_in));
    }

    int base64_decode_block(const char* code_in, const int length_in, char* plaintext_out, base64_decodestate* state_in) {
        return base64_decode_block_signed((int8_t *) code_in, length_in, (int8_t *) plaintext_out, state_in);
    }

    int base64_decode_chars(const char* code_in, const int length_in, char* plaintext_out) {
        return base64_decode_chars_signed((int8_t *) code_in, length_in, (int8_t *) plaintext_out);
    }

};
